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TABLE 4-2 Estimation of Minimum Daily Water Losses and Productiona

Reference

Source

Loss (mL/d)

Production (mL/d)

Hoyt and Honig, 1996

Respiratory loss

−250 to −350

 

Adolph, 1947b

Urinary loss

−500 to −1,000

Newburgh et al., 1930

Fecal loss

−100 to −200

Kuno, 1956

Insensible loss

−450 to −1,900

Hoyt and Honig, 1996

Metabolic production

 

+250 to +350

 

Total

−1,300 to −3,450

+250 to +350

Net loss

−1,050 to −3,100

 

a Assuming conditions in which there is minimal water loss from sweating.

4-2 displays estimated minimum losses and production of water (mL/day) in healthy sedentary adults, assuming conditions in which there is minimal water loss from thermoregulatory sweating. The following sections describe each source of water loss or production listed in this table.

Respiratory Water Loss

The amount of respiratory water loss, via evaporation within the lungs, is dependent on both the ventilatory volume and water vapor pressure gradient (Mitchell et al., 1972). Ventilatory volume is increased by physical activity, hypoxia, and hypercapnia, whereas the water vapor pressure is modified by the ambient temperature, humidity, and barometric pressure. Physical activity generally has a greater effect on respiratory water loss than do environmental factors. Daily respiratory water loss averages about 250 to 350 mL/day for sedentary persons, but can increase to 500 to 600 mL/day for active persons living in temperate2 climates at sea level (Hoyt and Honig, 1996). For these conditions, respiratory water loss (y = mL/day) can be predicted from metabolic rate (x = kcal/day) by the equation y = 0.107x + 92.2 (Hoyt and Honig, 1996). High altitude exposure (greater than 4,300 m, 448 mm Hg) can further increase respiratory water losses by approximately 200 mL/day (Hoyt and Honig, 1996).

2  

In general, dry bulb temperatures of approximately 70°F, 80°F, and 90°F are used for temperate, warm, and hot conditions, respectively, in this report.



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